Slime control in industrial waters

ABSTRACT

SLIME FORMATION IS CONTROLLED (E.G. RETARDED OR REMOVED) BY THE INTENTIONAL ADDITION TO INDUSTRIAL WATERS (E.G. WHITE WATER IN PULP AND PAPER MILLS) OF SLIME CONTROLLING AMOUNTS OF THE ENZYME LEVAN HYDROLASE.

US. Cl. 210-1 4 Claims ABSTRACT OF THE DISCLOSURE Slime formation is controlled (e.g. retarded or removed) by the intentional addition to industrial waters (e.g. white water in pulp and paper mills) of slime controlling amounts of the enzyme levan hydrolase.

BACKGROUND OF THE DISCLOSURE The formation of slime in industrial waters is a major industrial problem.

The term slime is a broad one covering a wide range of viscous, mucous, or leathery materials and mixtures found in industrial waters. Slimes are frequently polymeric in nature and can be broadly classified as chemical, biological, or composite slimes depending upon their cause or composition. For example, raw materials and equipment used in the paper industry are not sterile and water used in conjunction with such equipment is continuously being contaminated with a wide variety of microorganisms from such sources as wood pulp, chemicals, air, make-up --water, and the like. The existing conditions of temperature and the like permit the growth of a wide range of microorganisms. The growth of certain specific forms of these biological contaminants causes or produces polymeric excretions or products that are or become slime.

Historically, slime formation has been controlled by the addition to industrial waters (e.g. white water associated with the pulp and paper industry) of slimicides. The purpose of these slimicides is to destroy or arrest the growth of some of the many organisms present in the water to thereby prevent or retard the formation of slime. Slimicides (or toxicants as they are sometimes called) fall into two general categories; the first, biocides; and the second, biostats. Chemicals used as slimicides have included chlorine, phenylmercuric acetate, pentachlorophenol, tributyl tin oxide, and isothiocyanates, all of which are relatively toxic to humans.

Many workers have investigated the causes of slime formation in industrial waters and it is generally recognized that a broad spectrum of bacteria, predominately gram-negative bacteria, are responsible for the formation of slimes, particularly paper mill slimes. Yeasts and molds are lesser causes of slime than bacteria, particularly in paper mills. For example, although molds are easily isolated from industrial waters and cultivated in the laboratory, rapid natural fungal growth from mixed cultures in recirculating industrial waters has not been observed.

Those engaged in the search for slimicides or toxicants have periodically observed the lack of correlation between United States Patent the total bacterial counts and slime accumulation. Fre- SUMMARY OF THE INVENTION We have observed that levan (a specific type of fructose polymer which is produced by a wide variety of bacteria) c CC is a significant component of many industrial slimes. We have further discovered that it is difiicult and economically impractical to attempt to destroy or arrest the growth of all common bacteria that produce levan. We have found that slime accumulation can be controlled more readily by the addition of the enzyme levan hydrolase to the industrial water to thereby hydrolyze the leven produced by the bacteria. Although the enzyme may be used in conjunction with biocides and biostats, effective control over slime formation can be obtained by the mere use of this specific enzyme (i.e. levan hydrolase).

DETAILED DISCUSSION Industrial Waters and the Slime Problem Industrial waters comprise those waters used in indus trial plants for such purposes as conveying particulate material (e.g. paper pulp), cooling, and the like. Although the present invention is applicable to a wide range of in dustrial waters in which slime formation characteristically occurs, the present invention is particularly useful in the treatment of white water associated with pulp and paper mills. Consequently, the present invention will be described with particular reference to the treatment of slime formations in paper mill water systems without intending to be limited thereby.

Various persons have reviewed the slime problem in the paper industry caused by microorganisms present in white water. Attention is directed to the following articles and the references cited therein:

Coster, E., The Slime Problem in the Paper Industry Caused by Microorganisms, Appita 21, No. 4: 131-138 (January, 1968).

Leckey, C. R., The Slime Board Method of Paper Mill T oxicant Evaluation, Tappi 43, N0. 9: 781783 (September, 1960).

Michalski, R. J. et al., A Method for Determining the Effect of Dispersants in Slime Control Performance, Tappi 46, No. 2: l67a-l72a (February, 1963).

We have observed, as have prior workers, that the degree of slime formation cannot. be directly correlated with total microbial counts probably because white water contains a broad spectrum of microorganisms. However, the presence of a broad spectrum of microorganisms in such industrial waters is responsible for the activities of other workers in attempting to identify or produce chemicals having broad biocidical or biostatic properties.

In the course of our work, we found that a common type of polymer produced by many species of bacteria is a polysaccharide known as a levan. A levan is a polymer made up of fructose units joined by beta-2,6-linkages. We decided to approach the problem of slime accumulation by a direct attack on the slime, particularly upon levan, as opposed to an attack upon the organisms responsible for producing the slime.

THE ENZYME We have discovered that slime accumulation can be controlled or reduced by the addition to industrial waters containing levan-forming organisms by the addition to such waters of the enzyme levan hydrolase (sometimes called levan polyase).

The enzyme levan hydrolase is produced by a variety of microorganisms. It is possible that some of the enzyme is inherently produced in certain industrial water systems. This may account, in part, for the lack of correlation between total microbial count and slime formation. However, the conditions that exist in industrial waters such as white water do not ordinarily favor the production of Rhodotorula sp. Azotobacter sp. Bacillus sp.

Arthrobacter sp. Micrococcus sp. Pseudomonas sp.

The form of the enzyme will vary depending upon the particular source of the enzyme that is cultured. For example, levan hydrolase produced by Azotobacter sp. produces an extra-cellular enzyme whereas the yeast Rhodotorula sp. produces enzyme within or on the cell structure.

USE OF LEVAN HYDROLASE TO CONTROL SLIME ACCUMULATION Levan hydrolase is used to control slime accumulation by the intentional addition of the enzyme to industrial waters containing slime-forming microorganisms. The concentration of the enzyme can vary widely and will depend upon such factors as the type of industrial water being treated (e.g. white water), the conditions of treatment (e.g. temperature and pH of the water), the source of the enzyme (e.g. Rhodotorula sp.), and the enzyme activity. When using the enzyme in the form of dead cells of the yeast Rhodotorula sp. (at an activity of 20 units per gram), concentrations of from about 1 p.p.m. to 100 p.p.m. of the cells in water are effective. About 500 p.p.m., there is sometimes a tendency for the enzyme to discolor the water being treated. Good results are generally obtained at concentrations of 0.5-2O p.p.m. (eg. 1-10 p.p.m.). Such cells are conveniently used by drying the cells, diluting them with a salt (e.g. a metal sulfate such as sodium sulfate) to a concentration of, for example, ten percent by weight, and thereafter adding the resulting mixture to the water to be treated. If desired, the enzyme can be added to the water alone or mixed with other water additives (e.g. biocides, biostats, buffers, and the like).

The present invention is further illustrated by the fol lowing specific examples. Unless otherwise indicated, all parts and percentages are by weight.

EXPERIMENTAL PREPARATION OF THE ENZYME LEVAN HYDROLASE (a) Maintenance of Rhodotorula sp.)

Beef Extract (Difco)l0.0 Sucrose-50.0

Yeast Extract (Difco) 3.0 Sodium Chloride-5.0 Peptone (Difco)10.0

In making the slant medium, sufiicient distilled water was added to dissolve the above listed ingredients. The resulting solution was adjusted to pH 7.5 with 2.5 M sodium hydroxide and 1.2% /W.v. agar (Difco) was added. The suspension was then made up to volume with distilled Water. The agar was melted by heating the medium and boiling as short a time as necessary. The medium was dispensed in test tubes and sterilized at 121 C. for 20 minutes. The tubes were cooled in a slanted position to obtain a long slant and short butt.

The slant medium was inoculated from soil tubes and the cultures of Rhodotorula sp. were incubated at 30 C. for from four to five days before use.

(b) Preparation and Inoculation of Seed Medium Two ml. of a 5 ml. sterile water suspension of a fourto-five-day-old Rhodotorula culture was used to inoculate 50 ml. of seed medium in a 250 ml. baffled Erlenmyer flask. The seed medium contained the following ingredients in grams per liter of aqueous medium.

Sucrose20.0 Yeast Extract (Difco)-5.0 Black Strap Molasses-15.0 Peptone (Difco)12.0

The pH of the medium was adjusted to 6.7.

The medium was sterilized by autoclaving at 121 C. for 20 minutes and then cooled as rapidly as possible. After inoculation, the cultures were incubated on a incubator-shaker (New Brunswick Gyrotory Model G-25) operating at about 150 r.p.m. and 27 C. for 24-26 hours.

(c) Preparation and Inoculation of Inoculum Medium The contents of one 24-26 hour 50 ml. culture of seed growth was used to onoculate 500 ml. of inoculum medium in a two-liter bafiled Erlenmyer flask. The inoculum medium contained the following ingredients in grams per liter of aqueous medium:

Black Strap Molassesl00.0 Corn Steep Liquor20.0 Epsom Salts-0.6 Diammonium phos- Yeast2.5 phate-10.0

The solution was adjusted to pH 6.7, sterilized by autoclaving at 121 C. and cooled as rapidly as possible. After inoculation, cultures were incubated for 22-24 hours as described for the seed medium.

((1) Preparation and Inoculation of Production Medium The contents of two 22-24 hour 500 ml. cultures of inoculum growth was used to inoculate 8 kg. of production medium in a 14 liter fermentor. The fermentor was fully baflied and agitation was provided by means of two fixed vane, turbine-type, impellers 10 cm. apart and 10 cm. in diameter. Sterile air was introduced through a inch I.D. open pipe located directly beneath the bottom impeller. The fermentor was operated at an agitator speed of 700 r.p.m. with air flow at one volume per volume of medium per minute. The temperature was controlled at 27 C.:2 C. by means of a circulating water bath. Foam control was accomplished by the use of antifoam agents.

During the production phase, growth was monitored by measurement of pH and packed cell volumes. The latter were measured in calibrated conical centrifuge tubes. Levan hydrolase activity was measured by a modification of the tetrazolium chloride assay described by Avigad, et al. Levan substrate for the enzyme assay was prepared using Aerobacter levanicum according to the method of Avigad but isolation of the levan was omitted. The form of levan obtained in the isolation procedure is not decomposed appreciably by the enzyme produced by our strain of Rhodotorula. The enzyme assay procedure was as follows: Rhodotorula cells were separated from fermentor broth by centrifugation or by ethanol precipitation. The cells were diluted in 0.05 M morpholinopropane sulfonic acid buffer (pH 6.5). One ml. of diluted enzyme was added to each of three test tubes. The tubes were placed in a 40 water bath for five minutes. One ml. of substrate containing at least 10 micromoles of levan (determined as fructose) was added to the first two tubes, the third being used as a reagent blank. After exactly 30 minutes reaction time, 2.0 ml. of 0.5 M sodi- 1 Avigad, L., Ruth Zelikson, and S. Hestrin, Selective Determination 0] Sugars Manifesting Enediol Isomerism by Means 0] Reaction with Tetrazolium. Biochem. J. 80, 57-61 (1961).

Avigad, L., Methods in Carbohydrate Chemistry V, 161- 165. Academic Press, New York (1965).

urn hydroxide were added to all three tubes. Qne ml. of substrate 'was added to the reagent blank. Then 2.0 ml. of percent zinc sulfate heptahydrate were added to all tubes.;The--precipitate was removedby either filtration or centrifugation, and 1,0 ml. of the supernate was added to each of three test tubes. After adding 1.0 ml. of 1 percent 2,3,5-triphenyl- ZH-tetrazolium chloride, the tubes were placed in a 40 C. water bath for five minutes. Then 1.0 ml. of 0.5M NaOH was added to each tube. After exactly l5 minutes, 5 ml. of a 10 percent by volume glacial acetic acid in methanol solution was added to stop the reaction. The optical. density was read at 580 m in a spectrophotometer.

Tubes which contain a red precipitate in the above as say must be discarded and the cells diluted further for reassay. Units of- -activity per unit weight is defined as the product jof dilution factor and optical density at 580 millimicrons. Y J I When assays indicated that the yield of levan hydrolase reached a maximum, the fermentation was terminated and the cells of Rho'dotorula were collected.

(e) The'R ecovery of Levan Hydrolase A total weight of 45,300 grams of broth was collected from six production fermentors 44 hours after inoculation. The broth was passed through a separator which separated the broth into a wort phase and a yeast concentrate. The wort phase was diluted to the original volume of broth and again passed through the centrifuge. The yeast concentrates from the first and second centrifugations were combined. The second wort, which had a very low'yeast packed cell-volume, was discarded. The total yeast concentrate was diluted to 2.5 times its volume with water containing one percent of a non-ionic surfactant (commercially available as DC-161 from Economics laboratory, Inc. of St. Paul, Minnesota). It has been found that the activity and appearance of the final product is improved by the surfactant wash. The suspension was again passed through the separator and the wort discarded. The yeast concentrate was diluted with denatured alcohol (95% ethanol) until the alcohol concentration of the mixture reached 70%. A precipitate formed and was thereafter collected by filtration. The filtrate was discarded and the cake dried in a vacuum oven at 40 C. The cake was then ground to a fine powder (80 mesh). A total weight of 736 grams of yeast was collected having a levan hydrolase activity of 20 units per gram.

Experimental Procedures for Examples 1-5 The apparatusused in these examples was similar to that described by'Le'ckey. In this experimental system, paper mill white water (synthetic or natural) is passed over wood boards in such a manner as to encourage the build-up of a mass of wood pulp, insoluble inorganic materials and microbial cells. The mass is held together by bacterial slime so;-, that it is similar in nature to the substance found to be a problem in paper mills.

Two boxeswere used in these examples, one for testing theenzymeand onefor control purposes. Each box was built to accommodate five gallons of white water and fi'veslime boards positioned just above the surface of the water at an angle 'of inclination of about 45. The white watervvas runover the boards from a horizontal manifold attached to a submersible pump. Five holes in the manifold were located about two inches above the five boards. The flow rate of the Water from the manifold varied considerably depending upon slime accumulation, but averaged roughly 500 ml. per minute. In examples l-3, white water was obtained from a paper mill on a daily basis'l Theinitial' sampleconsisted of ten gallons to fill both boxes. Ther'eafte'r, one gallon of fresh white water was added after one gallon had been removed. The

fiLeckey, o. R., The Slime Board Method 0 Paper Mill Tomlcant Evaluation, TAPP I, 48, 781-783 (1960 latter was used for determination of microbial plate count, pH, and qualitative analysis for fructose. The temperatures of the boxes were allowed to reach their own levels to simulate the variable conditions found in paper mills. Average temperature values are given in the results. On some days, temperatures varied over as much as a ten degree range.

In order to allow for differences in box geometry and pumps, the box receiving the enzyme was alternated with each experiment. Enzyme was added according to apparent need.

Plate counts were made using the following medium at a pH of 6.7-7.0:

Plate Count Agar (Difco)-2.4 grams Brom Cresol Purple (alcoholic solution 1.6%)0.l ml. CaCI -H O (0.026% solution)--l.0 m1.

MgSO '7H O (0.05% solution)l.0 m1.

Distilled water to ml.

The medium was sterilized at 121 C. for 30 minutes.

All plates were incubated, after inoculation, at 45 C. for two days. Colonies were counted by means of a New Brunswick Colony Counter, Model C-llO.

Qualitative tests for fructose were made using the resorcinol-thiourea reagent method described by Avigad In this test, both fructose as levan and free fructose are detected if present. Samples were also examined for the presence of free fructose, alone, using 2,3,5-triphenyl-2H- tetrazolium chloride reagent ('I'IC). The latter reagent can also be used for detection of glucose, but the reaction can be made more specific for ketose sugars by the use of a short reaction time. A positive resorcinol test (levan plus free fructose) and a negative TTC test (free fructose, only), means that only levan is present.

In Examples 4 and 5, synthetic white water was sterilized and then inoculated with a known levan-producing bacterium, Aerobacter levanicum (ATCC No. 15552) to study the effect of Rhodotorula levan hydrolase cell concentration on bacterial slime in :a simulated paper mill system. Much more rapid experimental results can be obtained in this system than with natural paper mill white water. The synthetic white water contained the following ingredients in grams per liter:

Titanium dioxide-0.2 Animal glue-0.01 Wet strength resin-0.3 Sodium aluminate0.2 Rosin size-0.2

The pH of the synthetic white water was adjusted to pH 5.0 with technical grade sulfuric acid.

In Examples 4 and 5, each White water box was cleaned with 70 percent ethanol before addition of 20 liters of the sterile synthetic white water. The white water was then inoculated with 2 liters of A. levanicum culture. The bacteria for the inoculum were grown in one liter bafiled flasks containing 300 ml. of synthetic white water at 27 C. for 18 hours. All other aspects of Examples 4 and 5 were carried out as described for experiments with paper mill white water.

Thin layer chromatography on cellulose wasused to establish that the fructan observed in paper mill white water was identical, at least in part, to that formed by Aerobacter levan'icum, and that it was decomposed in the same manner as the bacterial levan.

The results of Examples 1-5 are setforth in the tables which follow. r 7

Example 1 Avigad, L., Methods in Carbohydrate Chemistry V, 161- 165. Academic Press, New York (1965).

8 Example 4 UN TREATED WHITE WATER This Example was run on Synthetic White Water Inoc- Colonies Resorcinolper ml. thiourea e W T m T I m 2 1 .m mm m 11 mm B V 00 E H C R n T r M W E R m e T ssaonooo a aorta m A A m mmmmmwww E mwww mmm a E 19 83810 I 70 y m T WP 222 2 W 2223 9.32 h I n .w a n W D w m E 1 6 D H EJ326856 M 3 548793 m l E 5677 77 77 67 77 7777 1 r M m w e d a E 52 31 "57 T Gav 1% m .C 44%44 44 E m w m m N m m e e U T Z m y A n N m a E e h n o n m N n u m m n a a a m n p M Wn n m 1 8H MA u 3 1 5 we e mmw 000000000 2km inv 0W8 y S w W? e r T atp m. mm a t 31.1331 0 7 7001s. n mmmmmmmwmw E wmwwmmmmwm wpw xxxxxxxxxx T xxxxxxxxxx m 3699926923 I 2 094384523 m aazrsrazra H zzaaaaaara ngd w mm D mmm E mw zsaasssssa 7&&7 7 7 7 7 7 7 e E dmm m. mm mumnuwwwwm E mmnummmawmw m M m m Y s z mam m w e mm n mrm n d nevm t EMd O5 a N2, d lem e a mmm Example 2 r This Example was run on White Water from a Cylinder Paper Machine of Paper Mill A.

Example 5 UNIREATED WHITE WATER This Example was run on Synthetic White Water Inoculated with Aerobacter levanicum (ATCC 15552).

TTC

Days of c T T w. .m% R C m a m Rm +++++mm+ A +++++mm M w s dd W dd mmmmmmmm E mmm ommm w mm needed T amen? E MN 33380 2 E 81287 H 0 2232 2 2 W H D W E D H 3184 2 9 M 98490 m 9 s77 && 7 E aazza E N n nwfifimmmm E MQMQMMMQ N m m U T Z N E u n t- "t 34 567891 5 4 M u I: 2 m m o a R N w m w .:++A +m+m+ e its 1111 W i auuvvwhmo m mwmwmmmm n mmmmmnmmm m XXXXXXXX T xxxxx x x 33903875 I 76858p9p1 h aazriaae H n w a s s v D 0 O h E N N h aaaaaarl E 4 5 6 454 7 7 d m m uwmnm mm E mwmfimw m w w M Y m. z m N e E m .Lm. m we m 0 0 m 1 g Example 3 This Example was run on White Water from a Fourdrinier Paper Machine of Paper Mill B.

" 5 p.p.m. enzyme added levan hydrolase activity of units/gram.

UNTREATED WHITE WATER The beneficial results which are Obtained can be understood by reference to tests run on white waterof Paper TTC Colonies Resorcinolper m1. thiourea Mill B (e.g. see Example 3). Slime removalfrom the boards and prevention of slime build-up was observed in the enzyme treated system as contrasted to the untreated system. In addition, a small difference in temperature between treated and untreated water was noticed with the lower temperature being obtained in the treated water.

8644555332 78&&&&&&&&

Considerable foam formation consistenly occurred in untreated water but was absent in the enzyme treated water.,

ENZYME TREATED WHITE WATER Similar results were obtained with the white water of Paper Mill A.

' 2. Processes of Claim wherein the enzyme i i e 300 p.p.m. enzyme added with levan hydrolase activity of 2 units/ tentionally added in the form" of d d; cells of yeast Rhodotorula sp.

gram."

10 3. Processes of Claim 2 wherein the Water is white OTHER REFERENCES water of a paper mill and the concentration of cells is Sanbom L R" Four steps to Control of Troublesome 1-1000 P-P- Outbreaks of Slime, Paper Trade Journal, vol. 149, Oct.

4. Processes of Claim 1 wherein the enzyme is period- 1 19 5 5 59 ically added to the water and the water is white water of 5 a paper mill. FRANK A. SPEAR, 111., Primary Examiner References Cited Us Cl XR UNITED STATES PATENTS 3,556,945 1/1971 Messing 195-63 10 UNITED S fAIL JS PATENT OFFICE CERTIFICATE OF 'CURBECTION Patent No. 3,824,184 Da July lg. 1914 Inventor-(s) Herbert Hatcher et a1 It is oertified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Column 3, Line 32 "About 5% should rea&.-- Above 500 p.p.m.--

In Column 3, Line 51, the parenthesis foliowing Rhodotorula 82. should be deleted o In Column 3, Line 56, "l.2%/w.v." should read In Column 4, Line 21, "onoculate" should read inoculate- Signed and sealed this 22nd day of October 1974.

'(sEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Arresting Officer Commissioner of Patents 

